I'm not sure I'd put one inside a house, but they'd be great on a porch (as shown below). I think it would be perfect for a beach house (unfortunately the in-law's beach house that I keep decorating in my head -- my FIL so gets steampunk -- just washed away with Hurricane Ike. Sigh.)
You would think there would be instructions for building one of these on Instructables, but the closest I found was this comment by the owner of the bed below, featured on Apartment Therapy: The suspended bed on our screened-in porch. It took about a day and cost less than $100 to build. Although I confess I didn't do much of the building — my husband and brother are responsible for that. I'm sure you could figure out how to build one, however.
Some of the most charming, old fashioned looking hanging beds are for sale at Bedzz without Legzzz.